Hypersensitivity

Anaphylactic reactions are rare, but may occur, especially in patients with a history of penicillin allergy.

Serum-sickness-like reactions are more frequent in pediatric patients and following a second or subsequent course of cefaclor and have been characterized by erythema multiforme, rash, arthritis, and/or arthralgia with or without fever.[Ref]

Renal

One case report of acute interstitial nephritis and nonoliguric renal failure has been reported following cefaclor therapy. (Reversible fever, azotemia, pyuria, and eosinophiluria are the hallmarks of cephalosporin-induced interstitial nephritis.)[Ref]

Renal side effects have included transient elevations in blood urea nitrogen (BUN) and serum creatinine in 0.2% of patients, reversible interstitial nephritis (rare), and abnormal urinalysis (0.5%). Extended-release cefaclor has been associated with increased BUN (0.2%), and increased creatinine (0.5%). Cephalosporins as a class have been associated with toxic nephropathy, reversible interstitial nephritis, and renal dysfunction.[Ref]

Genitourinary

Genitourinary side effects have included genital pruritus and vaginitis in less than 1% of patients. Extended-release cefaclor has been associated with vaginitis (2.4%) and vaginal moniliasis (2.2%), and dysmenorrhea, dysuria, leukorrhea, menstrual disorder, and nocturia in 0.1% to 1% of patients. Cephalosporins as a class have been associated with false-positive tests for urine glucose.[Ref]

Nervous system

Nervous system side effects have rarely included reversible hyperactivity, agitation, nervousness, insomnia, confusion, hypertonia, dizziness, hallucinations, and somnolence. Extended release cefaclor has been associated with headache in 4.9% of patients, and dizziness, insomnia, nervousness, somnolence, and tremor in 0.1% to 1% of patients, and paresthesia and vertigo. Some cephalosporins have been associated with seizures, primarily when dosages were not reduced in renally impaired patients.[Ref]

Other

Other side effects associated with extended-release cefaclor have included abdominal pain (1.6%), back pain (1%), and accidental injury, chest pain, chills, ear pain, fever, flu syndrome, infection, malaise, neck pain, otitis media, pain, and surgical procedure in 0.1% to 1% of patients. Cephalosporins as a class have been associated with abdominal pain, fever, and superinfection.[Ref]